1. Field of the Invention
The present invention relates to the field of semiconductor integrated circuits and more specifically to a CMOS integrated circuit wherein the PMOS and NMOS transistors have different dielectric properties.
2. Discussion of Related Art
Complimentary metal oxide semiconductor (CMOS) integrated circuits are widely used in logic applications such as in the design of very large scale integrated circuits such as microprocessor and microcontrollers.
As shown in FIG. 1, a CMOS integrated circuit 100 contains both n-type MOS (NMOS) transistors and p-type MOS (PMOS) transistors formed on a single substrate 106. NMOS device 102 is formed on a p-type conductivity region 108 of substrate 106 and contains a gate electrode 110 formed on a gate dielectric gate layer 112 and a pair of n-type source/drain regions 114 formed on laterally opposite sides of gate electrode 110. Similarly, PMOS device 104 is formed on a n-type conductivity region 116 of substrate 106 and contains the gate electrode 118 formed on gate dielectric layer 112 and a pair of p-type conductivity source/drain regions 120 formed along opposite sidewalls of gate electrode 118.
In CMOS architecture for digital applications, such as microprocessors, NMOS and PMOS devices 102 and 104, respectively, are operated in the "inversion mode" or they sit idle. To place PMOS transistor 104 in inversion mode, a negative gate voltage, V.sub.gs &lt;V.sub.t, is applied to gate electrode 118 of PMOS transistor 104 to form an inversion channel 122 of p-type conductivity between source/drain regions 120 which allows current to flow from one source/drain region 120 to the other source/drain region 120. To place NMOS device 102 in inversion mode, a positive gate voltage, V.sub.gs &gt;V.sub.t is applied to gate electrode 110 of transistor 102 to form and inversion channel 124 of n-type conductivity between source/drain regions 114 to allow currents to travel from one source/drain region 114 to the other source/drain region 114.
Although CMOS integrated circuits are generally more difficult to manufacture because they contain both PMOS and NMOS devices on a single substrate, CMOS devices are necessary in order to reduce power consumption, especially in very large scale (VLSI) circuits such as microprocessors where literally millions of transistors are coupled together.